Trial With Eribulin or Eribulin+ Endocrine Therapy in Locally-recurrent or Metastatic Breast Cancer Patients

Inclusion Criteria: * ER-positive and/or PR-positive breast cancer. * HER2-negative breast cancer. * Unresectable locally advanced or metastatic breast cancer. * Confirmed disease progression while in the last aromatase inhibition-containing regimen in the metastatic setting. * At least one taxane or anthracycline regimen in either the adjuvant or the neoadjuvant setting. * Patients with no prior line of chemotherapy in the metastatic setting. * At least 1 and up to 3 prior lines of endocrine therapy in the metastatic setting. * ECOG score 0 or 1. * Patients have adequate bone marrow and organ function. * Patients must have measurable disease (RECIST v.1.1). * Premenopausal with LHRH analogues for at least 28 days) and postmenopausal women. * Patients must agree to not breastfeed during the study and for 3 months after the last dose of study treatment. * Life expectancy greater or equal to 12 weeks. * Patients agree to collection of blood samples (liquid biopsy) and optional collection of metastatic tumour sample (biopsy) at the time of inclusion and progression (if appropriate). Exclusion Criteria: * Have received radiation therapy or limited-field palliative radiotherapy within two weeks prior to Cycle 1, Day 1, or patients who have not recovered from radiotherapy-related toxicities. * Have received prior chemotherapy for locally advanced or metastatic disease. * Have peripheral neuropathy grade 2 or greater. * QTc \> 480 msec on basal assessments, history of congenital or personal history of long QT syndrome, Brugada syndrome, or Torsade de Pointes (TdP), or uncontrolled electrolyte disorders * Child-bearing potential women not using highly effective methods of contraception. * Known hypersensitivity to eribulin, endocrine therapy or its excipients. * Other malignancies within the previous two years except adequately treated basal cell or squamous cell skin cancer or carcinoma in situ of cervix or breast. * Known uncontrolled metastases to the central nervous system (CNS) or any progressing CNS disease. * Have a serious concomitant systemic disorder incompatible with the study. * Major surgical procedure or significant traumatic injury within 28 days prior to randomization. * Have received any anti-cancer biology or investigational treatment within 30 days prior to randomization.